How to restrict or limit a new ubuntu user from accessing other folder?

1. add a new user

sudo adduser newuser

2. add user to sudo group

sudo usermod -aG sudo newuser

3. add user to ssh group

sudo vim /etc/ssh/sshd_config

>>AllowUsers newuser

4. add restriction to the new user (space sensitive)

sudo visudo -f /etc/sudoers.d/newuser

>>newuser ALL=(ALL) ALL, !sudoedit, !/usr/bin/su, !/bin/su, !/bin/bash, !/bin/sh, !/usr/bin/chmod, !/usr/bin/chown, !/usr/bin/docker, !/usr/bin/passwd, !/usr/sbin/visudo

5. check the new restriction

sudo visudo -c

If it is ok, you will the following message print out:

/etc/sudoers: parsed OK

/etc/sudoers.d/README: parsed OK

/etc/sudoers.d/newuser: parsed OK

6. apply folder restriction to current user folder

sudo chmod -R 700 /home/currentuser

7. reboot the machine and check the restriction

sudo reboot

cd /home/currentuser

sudo chmod -R 777 /home/currentuser

sudo docker ps

How to ssh or scp without password?

 

Method 1: Use SSH Key-Based Authentication

The most secure and recommended way is to set up SSH key-based authentication, which doesn't require you to include a password in the command.

1. Generate SSH Key Pair (if you don’t have one already):

    ssh-keygen -t rsa -b 4096

Save the key in the default location (~/.ssh/id_rsa).

2. Copy Public Key to the Remote Machine:

ssh-copy-id username@remote_host -p 22

Replace username and remote_host with your remote machine's username and IP address or hostname.

3. Run rsync without Password or ssh into another machine without Password:

rsync -avz /path/to/source/ username@remote_host:/path/to/destination/

ssh username@remote_host -p 22

4. Change folder permission on destination folder.

sudo chmod -R 777 destination_folder

How to install ffmpeg offline using a static version?

Ref: https://johnvansickle.com/ffmpeg/

1. What is a static build and how do I install it?

A static build is basically a binary with all the libs included inside the binary itself. There's no installation necessary in order to use a static binary, but you may want to place it in your shell's PATH to easily call it from the command line. Otherwise you can use the binary's absolute path. Here's a quick walkthrough:

Download the latest git build.

$ wget https://johnvansickle.com/ffmpeg/builds/ffmpeg-git-amd64-static.tar.xz

$ wget https://johnvansickle.com/ffmpeg/builds/ffmpeg-git-amd64-static.tar.xz.md5

With the build and the build's md5 hash downloaded you can check its integrity.

$ md5sum -c ffmpeg-git-amd64-static.tar.xz.md5
ffmpeg-git-amd64-static.tar.xz: OK

Unpack the build. Note: If you need to do this on Windows, use 7-Zip to unpack it. You may have to run it twice; once to uncompress and again to untar the directory.

$ tar xvf ffmpeg-git-amd64-static.tar.xz

Now I have the directory "ffmpeg-git-20180203-amd64-static".

$ ls ffmpeg-git-20180203-amd64-static
ffmpeg  ffprobe  GPLv3.txt  manpages  model  qt-faststart  readme.txt

Please read readme.txt! (hit "q" to exit out of "less")

$ less ffmpeg-git-20180203-amd64-static/readme.txt

Without any further steps I can start using ffmpeg with my relative path to the binary.

$ ./ffmpeg-git-20180203-amd64-static/ffmpeg
ffmpeg version N-89948-ge3d946b3f4-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 6.4.0 (Debian 6.4.0-11) 20171206
(snipped output to save space)

Or using the absolute path to the binary.

$ /home/john/ffmpeg-git-20180203-amd64-static/ffmpeg
ffmpeg version N-89948-ge3d946b3f4-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 6.4.0 (Debian 6.4.0-11) 20171206
(snipped output to save space)

To globally install it I need to move the binary into my shell's path. "PATH" is a variable in your environment set to a list of colon seperated directories the shell uses to locate binaries. Here's my system's path.

$ echo $PATH
/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin:/home/john/.local/bin:/home/john/bin

Your output may look different than mine, but it will be a somewhat similar list of directories. When I run the command "ffmpeg", the shell will look in /usr/local/bin first and then the next directory to the right in above list until it's found. If there's not a binary named "ffmpeg" in any of the above directories the shell will return "ffmpeg: command not found".


Before moving the ffmpeg binary into the shell's path, check to see if an older version of ffmpeg is already installed.

$ whereis ffmpeg 
ffmpeg: /usr/bin/ffmpeg

This lists an older version of ffmpeg in /usr/bin installed via my package manager. I can either uninstall the older version or place the newer static ffmpeg binary in a path that's searched before /usr/bin. According to my shell's path that would be /usr/local/bin.


Move the static binaries ffmpeg and ffprobe into the shell's path.

$ sudo mv ffmpeg-git-20180203-amd64-static/ffmpeg ffmpeg-git-20180203-amd64-static/ffprobe /usr/local/bin/

$ whereis ffmpeg
ffmpeg: /usr/local/bin/ffmpeg

$ whereis ffprobe
ffprobe: /usr/local/bin/ffprobe

Now ffmpeg is globally installed and you're done!

$ ffmpeg
ffmpeg version N-89948-ge3d946b3f4-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 6.4.0 (Debian 6.4.0-11) 20171206
  (snipped output to save space)

Uninstall.

$ sudo rm /usr/local/bin/ffmpeg /usr/local/bin/ffprobe

How to encode and decode character into ascii code?

 https://www.w3schools.com/tags/ref_urlencode.ASP

Character	From Windows-1252	From UTF-8
space	%20	%20
!	%21	%21
"	%22	%22
#	%23	%23
$	%24	%24
%	%25	%25
&	%26	%26
'	%27	%27
(	%28	%28
)	%29	%29
*	%2A	%2A
+	%2B	%2B
,	%2C	%2C
-	%2D	%2D
.	%2E	%2E
/	%2F	%2F
0	%30	%30
1	%31	%31
2	%32	%32
3	%33	%33
4	%34	%34
5	%35	%35
6	%36	%36
7	%37	%37
8	%38	%38
9	%39	%39
:	%3A	%3A
;	%3B	%3B
<	%3C	%3C
=	%3D	%3D
>	%3E	%3E
?	%3F	%3F
@	%40	%40

How to use docker registry locally?

 

How to print out ubuntu specs? Neofetch

sudo apt install neofetch -y

neofetch

neofetch --off (without any logo printed)

How to push the opencv result into a rtsp link?

1. download the rtsp server from this link and run it before step2 below, 

https://github.com/bluenviron/mediamtx/releases/download/v1.6.0/mediamtx_v1.6.0_linux_amd64.tar.gz

2. create an example main.cpp using the following code:-

#include <iostream>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/video.hpp>
#include <opencv2/videoio.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/core.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/imgproc.hpp>

using namespace cv;
using namespace std;

int main()
{

    //VideoWriter writer("appsrc ! videoconvert ! video/x-raw,format=I420 ! x264enc speed-preset=ultrafast bitrate=600 key-int-max=30 ! video/x-h264,profile=baseline ! rtspclientsink location=rtsp://localhost:8554/mystream",

    VideoWriter writer("appsrc ! videoconvert ! video/x-raw,format=I420 ! x264enc tune=zerolatency byte-stream=true threads=4 ! h264parse ! rtspclientsink location=rtsp://localhost:8554/mystream",
0,
15,
Size(1920, 1080),
true);

    VideoCapture cap("../sample_1080p_h265.mp4");
    //VideoCapture cap("rtsp://192.168.80.203");

    for (;;)
    {
        if (!cap.isOpened()) {
            cout << "Video Capture Fail" << endl;
            break;
        }

        Mat img;
        cap >> img;
        std::cout << "img shape: " << img.rows << ", " << img.cols << std::endl;

        //namedWindow("Display window", WINDOW_AUTOSIZE);// Create a window for display.
        //imshow("Display window", img);
        //waitKey(1);

        writer.write(img);
    }
}

3. create the CMakeLists.txt and build the program

cmake_minimum_required(VERSION 2.8)

project( main )

find_package( OpenCV REQUIRED )

include_directories( ${OpenCV_INCLUDE_DIRS} )

add_executable( main main.cpp )

target_link_libraries( main ${OpenCV_LIBS} )

4. view the live result using vlc, rtsp://localhost:8554/mystream